Radio frequency amplification system



Oct. 8, 1929, F". J. BULLWANT RADIO FREQUENCY AMPLIFICATION SYSTEM FiledNov. 5, 1925 Patented Oct. 8, 1929 UNITED STATES PATENT OFFICE FRANCISJ. BULLIVANT, ST. LOUIS, MISSOURI, ASSIGNOR TO VALLEY ELECTRIC COMPANY,OF ST. LOUls, MISSOURI, A CORPORATION OF DELAWARE RADIO FREQUENCYAMPLIFICATION SYSTEM Application filed November 5, 1925. Serial No.67,112.

This invention relates to radio frequency amplification systems and moreparticularly to inulti-stage systems utilizing audions or electrontubes.

One of the objects of this invention is to provide means for preventingundesirable oscillations in such a circuit, more especially in the rangeof higher wave lengths as now used in broadcasting.

Another object of this invention is to provide means for suppressing anysuch oscillations which may be or tend to set up and by a potentialaction rather than by'a capacity action.

Further objects will appear from the detail descriptiontaken inconnection with the accompanying drawing, in which:

Figure 1 is a diagram showing a radio. frequency amplification systemembodying this invention;

Figure 2 is a side elevation of a radio frequency transformer showingthe coupling element;

Figure 3 is a section on 2; and I i I Figure 4 is a detail showinganotherembodiment of this invention.

In an application of Victor H. Laughter, Serial NOFGTJOT tiled of evendate herewith, a coupling element is connected with the gr d of eachaudion in the radio frequency circuit of a radio frequency amplificationsystem and such coupling element is electro-magnetically as well aselectro-statically coupled with the plate circuit so as to apply to thegrida potential which is opposed to the potential of the disturbingoscillation. More specifically this coupling element comprises an openended coil which is magnetically as well as electro-statically coupledto the radio frequency transformer in the output circuit of the'audion,to the grid of which the coupling element is connected, and this coil isarranged for adjustment with respect to the transformerso as to providemeans for varying the potential impressed on the grid.

In accordance with this invention a coupling element is provided whichis coupled with the input circuit of one audion of the radio frequencycircuit and is connected with line 3-3, Figure the grid of thesucceeding audion. This coupling element is also preferably an openendedcoil, which in the specific embodiment disclosed is magnetically coupledwith the radio frequency transformer leading to the audion and isconnected with the grid of the succeeding audion so as to impress avoltage on that grid, The radio frequency transformer to which this coilis coupled is preferably the one preceding the first audion so that itis connected to the grid of the second audion. This coil is arranged foradjustment so as to vary the potential impressed on the grid, and sinceit is also electro-statically coupled to the transformer, it has anelectrostatic tapped coupling thereto so that by adjustment the voltageimpressed on the grid can be varied. I Referring now to the accompanyingdraw ing, and more particularly to Figure 1 which shows aradio-receiving system having two stages of radio frequency and twostages of audio frequency, 1 and 2 designate the amplifier tubes in theradio frequency circuit, the detector tube, and 4 and 5 the amplifiertubes in the audio frequency circuit. The audion tubes are of the usualform having a filament, a grid and a plate. The radio frequencytransformers are indicated at 10, 20

and 30, while the audio frequency transformers are indicated at 10 and50. Associated. with the input circuit of each tube is a variablecondenser indicated at 11,21 and 31. The usual grid leak and condenseris shown at 6 and the current controlling rheostats at 7 and 8.Condensers 12 and 22 may. also be provided. The usual connections to theaerial and ground and the A battery, B battery and battery are alsoindicated.

a As described in the Laughter application referred to, connected withthegrid of each of the audions 1 and 2 in the radio frequency circuit,is a coupling element 9, which as heretofore described, is preferably anopenended c0il. This coil is preferably magnetically coupled with theradio frequency transformer between the tube to whose grid it isconnected and the succeeding tube, and since it is in close proximitythereto, it is also electro-statically coupled with the transformercoils. The coil 9 is so wound that the voltage set up therein andin'ipressed on the grid will be opposed to the disturbing voltagesetting up the oscillation, so that the oscillation will be suppressed.it is furthermore adjustable in order to vary the magnitude of the impessed voltage in order to balance the objectionable voltage.

Coupled to the transforme 10 is a coupling element 13 which is connectedto the grid of the audion 2. This coupling element 13, as heretoforedescribed, is preferably an openended coil which is magnetically coupledwith the transformer and since it is in close proximity thereto, is alsoelectro-statically cou pled with the transformer coils. The coil thatthe voltage set up therein on the grid will be opposed to voltagesetting up the oscilla- .1 i -i18 ion, so that the oscillation will besuppressed. it is furthermore adjustable in oroer to vary the magni fileof the impressed voltage in i to buce the ob ectionable voltage,

is this invention is also applicable to frequency amplification systemscan radio p-oying cylindrical or solenoid coils, preferably toroidalcoils are used for the radio freuency transformers. Referring to Figures2 and 3, both the primary and secondary coils are shown as of toroidalform, the primary being made of sections 1a interposed by the sections15 of the secondary. These coils are held in proper assembled relationby endpieces 16 having notches 17 for engaging the c :il sections andheld together by screw 18 passing through a collar 19. Tape or ribbon252 may also be provided to further hold the parts together while theend plates are provided with feet for attaching the trans former to itssupport.

Each of the transformers 20 and has mounted thereon a balancing coil 9which is carried by a slotted bracket 26 supportingthe coil 9 and heldin adjusted position by a screw 2? taking into the end plate; this isfully deribed in the Laughter application referred to. The coil 13 isalso supported and adjustable in a similar manner on the transformer 10by a similar bracket 26 also held in adjusted position by ascrew 27taking into the end plate. In this way the coil 13 as well as the coil 9may be adjusted within the field set up bythe primary and secondarycoils. By moving the coils radially the voltages set up and impressed onthe grid can be varied and adjusted.

It will thus be seen that the invention ac complishes its objects. Theprovision of the coupling element- 13 impresses on the grid a voltagewhich will suppress the oscillations set up or tending to be set up. Byadjustment of this coil, the voltage impressed on the grid can be varieduntil the proper balance is obtained. The coil 13 is particularly usefulin 1 supplementing the actions of the coils 9 by sition and held inadjusted position.

suppressing oscillations, especially at the higher wave lengths as usedin broadcasting, for instance, above lOO meters. The direction ofwinding of the coil 13 can be readily determined in the same manner asfor the coil 9 as described in the Laughter application, for if wound inone direction it will cause suppression of the oscillation, while ifwound in the wrong direction the oscillation will not be completelysuppressed. In the diagram as shown in Figure 1 and Figures 2 and 3 theturns of the coupling coil 13 as in the coupling coil 9 are in the samedirection as those of the primary and secondary of the transformer towhich the coil is coupled. It is not, however, necessary to provide acondenser in the lead from either coil to the grid, for a voltage of theproper value can be readily obtained by adjustment of the coil. In viewof the fact that the coil 13 as well the coil 9 is an open-ended coil,the coupling to the transformer is an electrostatic as well as amagnetic coupling. Accordingly the phase as well as the magnitude of thevoltage applied to the grid is controllable as well as adjustable.Moreover since the coil is coupled electro-statica-lly as well aselectromagnetic-ally to the transformer coil or coils, the adjustmentprovides for varying the position of the coupled coil along the trans- Iformer coil so as to vary its relation to the potential gradient of thelatter coil and thereby adjust its potential elevation relativelythereto. lVhile the adjustment of the coil 13 is critical, the number ofturns of this coil is not critical in suppressing oscillations. However,by providing the coupling coil with a number of turns (twelve turns offine wire being found satisfactory for the coil 13 as well as the coil 9where the primary has twenty-one turns and the secondary one hundredsixty-five turns, and where the parts are of the relative dimension asshown, when using ordinary audions), the tone quality is improved;accordingly the combination results in a clean, pure tone with acomparatively wide range of selectivity. At the higher wave length thevolume as well as se any adjusted position. In this way the couplingcoil can be adjusted to the desired po- The coil 13 may also be placedbetween the coils 14; and 15.

lVhile certain theories have been advanced each having a grid withreference to the operation, it is to be understood that they are notabsolutely neces sary to the practical operation of this system;accordingly it is to be understood that this invention is not to belimited to any particular theory of operation. It is further obviousthat various changes may be made in details of construction withoutdeparting from the spirit of this invention; it is, therefore, to beunderstood that this invention is not to be limited to the specificdetails shown and described.

Having thus described the invention, what is claimed is:

1. A multi-stage radio-frequency amplification system comprising, aplurality of audions each having a grid and a plate, input and outputcircuits, a coil in the input circuit of an audion, and a coilmagnetically and electrostatically coupled to said first coilintermediate its ends and connected to the grid of the succeedingaudion, said latter coil being adjustable relative to said first coil.

2. A multi-stage frequency amplification system, comprising, a pluralityof audions and a plate, input and output circuits, transformer coils insaid circuits, a coil magnetically and electrostatically coupled to theoutput coil of one of said audions and connected to the grid thereof, acoil magnetically and electrostatically coupled to the input coil of apreceding audion and connected to said same grid, and means foradjusting said coupled coils relatively to their respective transformercoils.

3. A multi-stage amplification system, comprising, a plurality ofaudions each having a grid and a plate, input and output circuits, acoil in the input circuit of an audion, a coil magnetically andelectrostatically coupled with said coil and connected with the grid ofthe succeeding audion, a coil in the output circuit of said secondaudion, and a coil magnetically and electrostatically coupled with saidthird coil and connected with said grid of said second audion, one ofsaid grid circuit coils being adjustable relative to its coupled coil.

In testimony whereof I affix my signature this 4th day of September,1925.

FRANCIS. J. BULLIVANT.

